A variety of micro-electro-mechanical systems (MEMS) switches are in use in radar and communication systems as well as other high frequency circuits for controlling RF signals. Many of these MEMS switches generally have electrostatic elements, such as opposed electrodes, which are attracted to one another upon application of an actuation voltage (e.g., from a DC voltage source), resulting in the establishment of a high capacitive coupling and/or reduced electrical impedance between spaced apart signal electrodes. Thus, a signal is allowed to propagate between the spaced apart signal electrodes.
In the capacitive-type MEMS switch, a dielectric layer is deposited on top of a first signal electrode and underneath a second moveable signal electrode. With this arrangement, the full actuation voltage may appear across the dielectric layer resulting in a high electric field across the dielectric layer. This high field can lead to charge accumulation on the dielectric surface as well as in the bulk dielectric (also known as the dielectric charging effect), which can lead to switch failure and/or reliability issues from stiction and/or degradation of capacitance values. Contact-type MEMS switches have utilized dielectric layers between the top and bottom actuation electrodes to prevent electrical shorting of the actuation electrodes, and these dielectric layers between the top and bottom actuation electrodes may encounter similar problems from the dielectric charging effect, which can lead to device reliability issues and/or performance degradation.
Prior designs have utilized dielectric or metal bumps on the actuation electrode in an attempt to prevent stiction, but the dielectric bump has trapped charge, and the metal bump has caused issues with the floating voltage potential. Accordingly, improved MEMS switches and methods of fabricating such MEMS switches are desired.